The present invention relates to a sputtering target for a magnetic recording film, which is used in the deposition of a magnetic thin film of a magnetic recording medium, and particularly a magnetic recording layer of a hard disk adopting the perpendicular magnetic recording system; and to a sputtering target capable of inhibiting the formation of cristobalites that cause the generation of particles during sputtering, and shortening the time required from the start of sputtering to deposition (hereinafter referred to as the “burn-in time”).
In the field of magnetic recording as represented with hard disk drives, a material based on Co, Fe or Ni as ferromagnetic metals is used as the material of the magnetic thin film being responsible for the recording. For example, Co—Cr-based or Co—Cr—Pt-based ferromagnetic alloys having Co as its main component are used for the recording layer of hard disks adopting the longitudinal magnetic recording system.
Moreover, composite materials of a Co—Cr—Pt-based ferromagnetic alloy having Co as its main component and a nonmagnetic inorganic material are often used for the recording layer of hard disks adopting the perpendicular magnetic recording system which was recently put into practical application.
A magnetic thin film of a magnetic recording medium such as a hard disk is often produced by sputtering a target of ferromagnetic material having the foregoing materials as its components in light of its high productivity. Moreover, SiO2 is sometimes added to such a sputtering target for a magnetic recording film in order to magnetically separate the alloy phase.
As a method of manufacturing a ferromagnetic sputtering target, the melting method or powder metallurgy may be considered. It is not necessarily appropriate to suggest which method is better since it will depend on the demanded characteristics, but a sputtering target composed of ferromagnetic alloys and nonmagnetic inorganic grains, which is used for forming the recording layer of hard disks based on the perpendicular magnetic recording system, is generally manufactured with powder metallurgy. This is because the inorganic grains such as SiO2 need to be uniformly dispersed within the alloy basis material and this is difficult to achieve with the melting method.
For example, proposed is a method of: mechanically-alloying an alloy powder having an alloy phase prepared by the rapid solidification method, and a powder configuring the ceramic phase, so that the powder configuring the ceramic phase is to be uniformly dispersed within the alloy powder; and performing hot press molding thereto in order to obtain a sputtering target for use in a magnetic recording medium (Patent Document 1).
The target structure in the foregoing case appears to be such that the base metal is bonded in a milt (cod roe) shape and surrounded with SiO2 (ceramics) (FIG. 2 of Patent Document 1), or SiO2 is dispersed in a thin string shape (FIG. 3 of Patent Document 1). While it is blurred in the other diagrams, the target structure in such other diagrams is also assumed to be of the same structure. This kind of structure entails the problems described later, and it cannot be said that this kind of structure is a preferred sputtering target for a magnetic recording medium. Note that the spherical substance shown in FIG. 4 of Patent Document 1 is mechanical alloying powder, and is not a structure of the target.
Moreover, without using the alloy powder prepared by the rapid solidification method, it is also possible to produce a ferromagnetic sputtering target by preparing commercially available raw powders for the respective components configuring the target, weighing these raw powders to achieve the intended composition, mixing the raw powders with a known method such as ball milling, and molding and sintering the mixed powder via hot press.
There are various types of sputtering devices, but a magnetron sputtering device comprising a DC power source is broadly used in light of its high productivity for the deposition of the foregoing magnetic recording films. This sputtering method is to place a positive-electrode substrate and a negative-electrode target opposite each other, and generate an electric field by applying high voltage between the substrate and the target under an inert gas atmosphere.
Here, inert gas is ionized, plasma composed of electrons and positive ions is formed, the positive ions in the plasma collide with the target (negative electrode) surface to discharge the constituent atoms of the target, and the extruded atoms adhere to the opposing substrate surface to form a film. The sputtering method employs a principle where the material configuring the target is deposited on the substrate as a result of performing the sequential process described above.
As described above, the sputtering target for a magnetic recording film is sometimes doped with SiO2 in order to magnetically separate the alloy phase. When SiO2 is added to the magnetic metal material, there is a problem in that micro cracks are generated in the target and the generation of particles during sputtering increases.
Moreover, with a SiO2-doped magnetic material target, there is an additional drawback in that the burn-in time becomes longer in comparison to a magnetic material target that is not doped with SiO2.
While there was some debate as to whether this was due to problems related to the SiO2 itself, or due to the transformation of SiO2, or due to problems related to the interaction with other magnetic metals or additive materials; the fundamental cause had not been clarified. In most cases, the foregoing problems were considered inevitable and were quietly condoned or overlooked. Nevertheless, it is necessary to maintain the characteristics of magnetic films at a high level based on current demands, and the further characteristic improvement of sputtered film is being demanded.
With conventional technologies, certain documents describe the technique of adding SiO2 to a sputtering target using a magnetic material. Patent Document 2 discloses a target including a metal phase as a matrix, a ceramic phase that is dispersed in the matrix phase, and an interfacial reaction phase between the metal phase and the ceramic phase, wherein the relative density is 99% or more. While SiO2 is included as an option as the ceramic phase, Patent Document 2 has no recognition of the foregoing problems and fails to propose any solution to such problems.
Patent Document 3 proposes, upon producing a CoCrPt—SiO2 sputtering target, calcining Pt powder and SiO2 powder, mixing Cr powder and Co powder to the obtained calcined powder, and performing pressure sintering thereof. Nevertheless, Patent Document 3 has no recognition of the foregoing problems and fails to propose any solution to such problems.
Patent Document 4 discloses a sputtering target including a metal phase containing Co, a ceramic phase having a grain size of 10 μm or less, and an interfacial reaction phase between the metal phase and the ceramic phase, wherein the ceramic phase is scattered in the metal phase; and proposes that SiO2 is included as an option as the ceramic phase. Nevertheless, Patent Document 4 has no recognition of the foregoing problems and fails to propose any solution to such problems.
Patent Document 5 proposes a sputtering target containing non-magnetic oxide in an amount of 0.5 to 15 mol, Cr in an amount of 4 to 20 mol, Pt in an amount of 5 to 25 mol, B in an amount of 0.5 to 8 mol, and remainder being Co. While SiO2 is included as an option as the non-magnetic oxide, Patent Document 5 has no recognition of the foregoing problems and fails to propose any solution to such problems.
Note that Patent Document 6 is also listed as a reference, and this document discloses technology of producing cristobalite grains as filler of sealants for semiconductor elements such as memories. While Patent Document 6 is technology that is unrelated to a sputtering target, it relates to SiO2 cristobalites.
Patent Document 7 relates to a carrier core material for use as a electrophotographic developer. While Patent Document 7 is technology that is unrelated to a sputtering target, it relates to the types of crystals related to SiO2. One type is SiO2 quartz crystals, and the other type is cristobalite crystals.
While Patent Document 8 is technology that is unrelated to a sputtering target, it explains that cristobalite is a material that impairs the oxidative protection function of silicon carbide.
Patent Document 9 describes a sputtering target for forming a protection film of an optical recording medium having a structure where patternless SiO2 is dispersed in the zinc chalcogenide base metal. Here, the transverse rupture strength of the target comprising zinc chalcogenide-SiO2 and the generation of cracks during sputtering with such target are affected by the form and shape of SiO2, and Patent Document 9 discloses that when the SiO2 is patternless (amorphous), the target will not crack during sputtering, even with high-power sputtering.
While this is a suggestion in some ways, Patent Document 9 consistently relates to a sputtering target, using zinc chalcogenide, for forming a protection film of an optical recording medium, and it is totally unknown as to whether it can resolve the problems of a magnetic material having a different matrix material.    [Patent Document 1] Japanese Laid-Open Patent Publication No. H10-88333    [Patent Document 2] Japanese Laid-Open Patent Publication No. 2006-45587    [Patent Document 3] Japanese Laid-Open Patent Publication No. 2006-176808    [Patent Document 4] Japanese Laid-Open Patent Publication No. 2008-179900    [Patent Document 5] Japanese Laid-Open Patent Publication No. 2009-1861    [Patent Document 6] Japanese Laid-Open Patent Publication No. 2008-162849    [Patent Document 7] Japanese Laid-Open Patent Publication No. 2009-80348    [Patent Document 8] Japanese Laid-Open Patent Publication No. H10-158097    [Patent Document 9] Japanese Laid-Open Patent Publication No. 2000-178726